In general, when a thermoplastic resin is molded by an injection molding or compression molding, in order to avoid elongation of time in a molding cycle due to change in temperature of the mold, molding is carried out at a marginal temperature range which barely permits the melt to be filled into the mold and the product taken out from the mold without deformation.
Further, when a thermoplastic resin is subjected to an injection molding, if the temperature of the mold is kept at a high temperature upon filling the melt into the mold, since the fluidity of the resin is improved, it becomes possible to take an advantage in forming the product into a thin-walled product as well as in improving replication property, i.e., how well the shape of the cavity surface is replicated to the surface of the product. In addition, a weld line becomes not conspicuous. Thus, many inventions have been made on a matter that heat is exclusively applied to the cavity surface during injection of the melt into the mold.
For example, a method in which heating is effected by heated air is disclosed in Japanese Examined Patent Publication Gazette No. 22020/1970; a method of combination in which heating is effected by an electric heater and cooling by cooled water is disclosed in Japanese Patent Laid-open Publication Gazette No. 22759/76; a method in which heating is effected by high frequency induction is disclosed in Japanese Patent Laid-open Publication Gazette No. 109639/1980; a method in which heating is effected by supplying steam into a cavity is disclosed in Japanese Patent Laid-open Publication Gazette No. 165229/1982; a method in which heating is effected by interposing a heated plate between a cavity and a core is disclosed in Japanese Patent Laid-open Publication Gazette No. 79614/1986; a method in which heating is effected by a halogen bulb is disclosed in Japanese Patent Laid-open Publication Gazette No. 42217/1989; and a method in which heating is effected on a cavity surface by an electricity conducting layer is disclosed in Japanese Patent Laid-open Publication Gazette No. 265720/1992.
Further, a method in which heating is effected by supplying a heating medium such as steam, hot water or hot oil into a circuit commonly utilized to a cooling medium is disclosed in Japanese Patent Laid-open Publication Gazettes No. 55219/1981, No. 12739/1983, No. 54828/1985, and No. 193223/1997. Furthermore, as an improvement of the above proposals, a method in which heating is effected by using two piping systems of heating medium circuit is disclosed in Japanese Patent Laid-open Publication Gazette No. 100867/1995, a method in which heating medium and cooling medium are independently supplied from respective tanks and recovered to the same is disclosed in Japanese Patent Laid-open Publication Gazette No. 215309/1983; a method in which a piping system is arranged so that a portion of the circuit commonly utilized by the heating medium and cooling medium is made small as far as possible is disclosed in Japanese Patent Laid-open Publication Gazette No. 208918/1987; a method in which a medium is heated amid the circuit of the medium only when a mold is to be heated, is disclosed in Japanese Patent Laid-open Publication Gazette No. 269515/1989; and a method in which heating is effected by heated water flowing through a closed loop is disclosed in Japanese Patent Laid-open Publication Gazette No. 37108/1981.
The above-described method in which heating is effected by heated air suffers from a problem that a heating capacity is small. The method in which heating is effected by an electric heater and the method in which the cavity surface is heated by an electricity conducting layer encounters a problem that the apparatus thereof becomes complicated and expensive. The method in which heating is effected by high frequency induction also encounters a problem that it takes a lot of time to insert or take out a heating device and the apparatus thereof becomes expensive. The method in which steam is supplied into the cavity encounters a problem that the method is applicable only to a situation where a cavity becomes wet will not cause any problem. The method in which the heated plate is interposed between the cavity and the core and the method in which heating is effected by a halogen bulb, suffer from a problem that it takes a lot of time to insert or take out a heating device, in addition to time to take off a product.
Furthermore, the method in which heating and cooling are effected by using a common circuit encounters the following problem. That is, if the circuit is remote from a cavity surface, then the mold is heated and cooled not only at the surface portion but also at the deep portion of the mold, and hence heating and cooling are excessively carried out, with the result that it takes a lot of time for switching between the heating mode and the cooling mode, and responsibility in heating and cooling becomes deteriorated.
Further, according to the method in which heating is effected by using two piping systems of heating medium fluid passage as an improvement of the above-described method, a first heating medium channel provided near a cavity surface is supplied with a heating medium upon heating the mold and supplied with a cooling medium upon cooling the mold while a second heating medium channel provided at a place remote from the cavity surface is supplied with a heating medium, cooling medium or air upon heating the mold and supplied with a cooling medium upon cooling the mold, whereby it is intended to shorten a molding time. However, the second heating medium channel hardly achieves the intended purpose and rather the arrangement causes a problem that it takes a lot of processes in forming the fluid passage within the mold.
According to the other improvements, i.e., the method in which the heated medium and the cooled medium are independently supplied from respective tanks and recovered to the same, the method in which the portion of the circuit commonly utilized by the heated medium and cooled medium is made small as far as possible, the method in which the medium is heated amid the circuit of the medium only when a mold is to be heated, and the method in which heating is effected by heated water flowing through a closed loop, are not intended to improve the heating and cooling system within the mold but such one that the heating and cooling system within the mold is left unchanged from a conventional arrangement but a portion other than the mold is improved to shorten the molding cycle.
Accordingly, an object of the present invention is to provide a synthetic resin molding mold in which it becomes possible with ease to carry out switching between the heating mode and the cooling mode for heating and cooling a cavity surface within the mold with a short period of time.
Another object of the present invention is to provide a synthetic resin molding mold from which it becomes possible to obtain a product without any deformation and surface defect.
Further object of the present invention is to provide a synthetic resin molding mold in which it becomes possible to avoid fatigue of the mold caused by the switching between the heating mode and the cooling mode of the mold.
Still further object of the present invention is to provide a synthetic resin molding mold in which it becomes possible to lessen a heating flow to a mold base while quickening the increase in temperature of the cavity surface.